1. Technical Field
The present invention relates to a method for surface-treating a printed circuit board and a printed circuit board including a surface treatment layer manufactured by the method.
2. Description of the Related Art
Recently, an immersion tin plating method and the use of silver and organic solderability preservative (OSP) are required in a printed circuit board (PCB) field, due to an increase in cost of raw material for gold plating in surface treatment. Among them, a method using the organic solderability preservative is increasingly used since it has advantages in view of unit cost as well as management.
FIG. 1 is a view schematically showing a procedure of surface-treating a printed circuit board according to the related art. First, a substrate treated with plasma is surface-treated by using a method using an organic solderability preserve. A solder paste is printed on the surface-treated substrate, followed by a reflow curing process and a deflux washing process.
Among surface treatment methods, the method using an organic solderability preserve, in spite of the above advantages, has problems in that thermal damage occurs after a reflow process and an organic solderability preserve film is removed after the deflux washing process, since components of the organic solderability preserve are made of an organic material.
In other words, about 70% of the organic solderability preserve film is removed while the reflow process is performed after an organic solderability preserve surface treatment process, and about 90% or more is removed after the deflux process. Due to this, Cu is exposed, and the exposed Cu reacts with oxygen in the air, thereby generating CuO and Cu2O as copper oxide. In the copper oxide, when CuO is exposed to a copper pad, discoloration occurs.
For a specific example, bare Cu, in which all of the organic solderability preserve film is removed, is bound to oxygen and oxidized to cause incomplete combustion, thereby forming Cu2O exhibiting a brown color with yellow-red (see, FIG. 2). Here, the reaction equation is that 4Cu+O2→2Cu2O, and a surface SEM photograph thereof is shown in FIG. 3.
In addition, the bare Cu is bound to oxygen and oxidized, and thus completely combusted, thereby forming CuO exhibiting a black-red color (see, FIG. 4). Here, the reaction equation is that 2Cu+O2→2CuO, and a surface SEM photograph thereof is shown in FIG. 5.
Here, Cu2O does not substantially incur a defect of discoloration, but CuO incurs severe discoloration as shown in FIG. 4.
Therefore, there needs a method for solving the discoloration problem due to CuO, which is formed by oxidation of copper occurring during surface treatment of the printed circuit board.